// GenericsNote: Converted.
/*
 *  Copyright 2001-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections15.functors;

import java.io.Serializable;

import org.apache.commons.collections15.Transformer;

/**
 * Transformer implementation that returns the same constant each time.
 * <p/>
 * No check is made that the object is immutable. In general, only immutable
 * objects should use the constant factory. Mutable objects should use the
 * prototype factory.
 *
 * @author Matt Hall, John Watkinson, Stephen Colebourne
 * @version $Revision: 1.1 $ $Date: 2005/10/11 17:05:24 $
 * @since Commons Collections 3.0
 */
public class ConstantTransformer<T>
		implements Transformer<Object, T>, Serializable {

	/**
	 * Serial version UID
	 */
	static final long serialVersionUID = 6374440726369055124L;

	/**
	 * Returns null each time
	 */
	public static final Transformer NULL_INSTANCE = new ConstantTransformer(
			null);

	/**
	 * The closures to call in turn
	 */
	private final T iConstant;

	/**
	 * Transformer method that performs validation.
	 *
	 * @param constantToReturn
	 *            the constant object to return each time in the factory
	 * @return the <code>constant</code> factory.
	 */
	public static <T> Transformer<Object, T> getInstance(T constantToReturn) {
		if (constantToReturn == null) {
			return NULL_INSTANCE;
		}
		return new ConstantTransformer<T>(constantToReturn);
	}

	/**
	 * Constructor that performs no validation. Use <code>getInstance</code> if
	 * you want that.
	 *
	 * @param constantToReturn
	 *            the constant to return each time
	 */
	public ConstantTransformer(T constantToReturn) {
		super();
		iConstant = constantToReturn;
	}

	/**
	 * Transforms the input by ignoring it and returning the stored constant
	 * instead.
	 *
	 * @param input
	 *            the input object which is ignored
	 * @return the stored constant
	 */
	@Override
	public T transform(Object input) {
		return iConstant;
	}

	/**
	 * Gets the constant.
	 *
	 * @return the constant
	 * @since Commons Collections 3.1
	 */
	public T getConstant() {
		return iConstant;
	}

}
